In the information age, its very easy to be discovered. The people who need it most are aware of the problem and looking for solutions. They will search and find you if you have decent SEO, or you are listed in the top catalogs/places people search.

Customers will make their own ads for your product (sharing their positive experience on social media, etc.)

Agree that some products need ads to make people buy them. But, I'd rather not sell those kinds of products.